There are multiple ways to deposit functional polymer films. Spin coating has been used extensively in the field of electronics for its ability to spread solution-processable materials in smooth films over large areas. In most polymer deposition processes, liquid solvents are used in order to enhance the processability of the materials and simplify their handling. Typically, one kind of material is deposited per coat, usually on an atomically flat substrate, such as silicon. During the spin-coating process, the solvent is quickly removed via centrifugal forces to leave behind a film having a desired thickness, which can be further dried with a brief bake step. If a particular application requires a stack of two different polymers, (e.g., Polymer B on top of Polymer A), attention must be paid to the interaction of Solvent B with the dry film of Polymer A. If Solvent B is miscible with Polymer A, the result is usually a significant amount of swelling, intermixing or damage to the film of Polymer A that may be undesirable for many applications.
As the field of high-resolution patterning progresses towards the molecular realm, alternative patterning techniques offer cost-attractive process options to expensive lithography tools. Of these methods, the self-assembly of block copolymers is a method for extending lithographic patterning into the sub-20 nm size regime.
The block copolymer community has been limited to the use of only one block copolymer per layer due to the damage and intermixing caused by the spin coating of another block copolymer solution on top of a previously deposited copolymer film. The limitation of only one self-assembled block copolymer domain size and pitch is not attractive to the lithography community, which has grown used to the ability to print patterns of arbitrary shapes and sizes using photolithography.